Optical Module

ABSTRACT

An optical module which can achieve miniaturization, high performance and cost reduction is provided. The optical module includes a photoelectric component, a high-speed signal processing part which processes a high-speed signal photoelectrically converted by the photoelectric component, and a low-speed signal processing part which processes a low-speed signal. The high-speed signal processing part and the low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an optical module, and moreparticularly to an optical module for performing photoelectricconversion in a high-speed optical communication system.

2. Description of the Related Art

Recently, transmission rates required in optical communication systemsare being increased with an increase in the amount of data to betransmitted. Additionally, it is required to reduce sizes and costs ofapparatuses provided in the optical communication systems. Particularly,in high-speed optical communication systems, it is highly required toachieve miniaturization, high performance and lower costs of opticalmodules used for photoelectric conversion.

Many attempts have been made to reduce sizes and costs of devices usedin low-speed communication systems by integrating circuits and usingbare chips and discrete components together. Additionally, attempts havebeen started to reduce sizes and costs of devices used in medium-speed(2.4 Gbps, for example) communication systems. The techniques to achievethe miniaturization, high performance and lower costs of the deviceshave been applied to the optical modules.

FIG. 1 shows an example of a conventional optical module. In FIG.1, acase 100 is made of metal and has a rectangular parallelepiped shapewhose top surface is opened. A lid 110 is also made of metal and has ashape which can be engaged inside the case 100. An optical fiber cable130 for inputting optical signals is connected to an optical component120. The optical component 120 is fixed to the case 100 by a metalmount. Signals outputted from the optical component 120 are supplied toa printed-circuit board 140.

A high-speed circuit part 150 comprising a ceramic package is providedon the printed-circuit board 140. The printed-circuit board 140processes low-speed signals and a part of high-speed signals. On theother hand, the high-speed circuit part 150 is dedicated to process thehigh-speed signals. The signals which are photoelectrically converted bythe optical component 130 are so weak that the printed-circuit board 140and the high-speed circuit part 150 are needed to be electricallyshielded. Thus, the lid 110 is mounted inside the case 100 and sealed byseam welding so that the printed-circuit board 140 and the high-speedcircuit part 150 are electrically shielded.

The seam welding is an electric resistance welding method used toconnect metal members. Although the seam welding has an advantage thatchips provided inside the package are not substantially heated, it has adrawback that the cost is high. However, characteristics of a surfaceacoustic wave (SAW) filter provided in the high-speed circuit part 150are unstable and a required specification is not satisfied unless theSAW filter is used in a sealed structure. Additionally, although an ICcontaining a phase-locked loop (PLL) circuit may be substituted for theSAW device, such an IC has poor noise resistance and reliability ascompared to the SAW filter. Thus, the seam welding is advantageouslyused to seal the case 100 and the lid 110, resulting in a high cost ofthe sealing.

Additionally, if all of the circuits are provided in a package to besealed, a size of the package becomes large and thus the miniaturizationand the cost reduction cannot be achieved.

Further, amplifiers used in an optical module which operates at atransmission rate of several Gbps are required to have a wide-rangeamplifying characteristic ranging from several tens of kHz to severalGHz since an optical communication system generally uses a base bandtransmission. Thus, it is necessary to suppress impedance mismatch andgeneration of heat, which may be tolerated in a case of a low-speedtransmission system, so that the wide-range amplifying characteristic isnot degraded at a part connecting the optical component and thehigh-speed electric amplifier.

Still further, if a phase balance between the IC in the package to besealed and the SAW filter is changed during the sealing process, fineadjustments of phase cannot be performed. Additionally, impedancemismatch occurs when a high-frequency transmission path passes throughmany layers of a multilayered board between the optical component and amain board.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoptical module which can achieve miniaturization, high performance andcost reduction.

The above object of the present invention is achieved by an opticalmodule comprising:

a photoelectric component;

a high-speed signal processing part which processes a high-speed signalphotoelectrically converted by the photoelectric component; and

a low-speed signal processing part which processes a low-speed signal,wherein

the high-speed signal processing part and the low-speed signalprocessing part are overlapped with each other in a vertical directionand electrically connected to each other.

In this invention, since the high-speed signal processing part and thelow-speed signal processing part are separated from each other, thenumber of components to be sealed in the package can be decreased andthus the cost of the optical module can be reduced. Additionally, sincethe low-speed signal processing part and the high-speed signalprocessing part are overlapped with each other in a vertical direction,the optical module can be miniaturized. Further, since the low-speedsignal processing part can be mounted on a multipurpose printed circuitboard, double-sided surface mount can be used, and thus theminiaturization and the cost reduction can be achieved furthereffectively.

Additionally, the high-speed signal part may comprise a high-speedsignal input part for inputting the high-speed signal, a high-speedsignal processing circuit part for processing the high-speed signalinputted to the high-speed signal input part, and a high-speed signaloutput part for outputting the signal processed by the high-speed signalcircuit part.

In this case, each of the high-speed signal output part and high-speedsignal circuit part may comprise a multilayered board, the multilayeredboard of the high-speed signal output part having a length correspondingto a distance between the high-speed signal circuit part and a mainboard and being connected to the multilayered board of the high-speedsignal circuit part so that the layered directions of the multilayeredboards are perpendicular to each other.

In this invention, since the layered directions of the multilayeredboard of the high-speed signal output part and the high-speed signalcircuit part are perpendicular to each other, signals from thehigh-speed signal circuit part always flow along the layers of themultilayered board to the main board, and thus impedance matching can beeasily achieved.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a conventional optical module;

FIG. 2 shows a side view of an embodiment of an optical module accordingto the present invention;

FIG. 3 shows a schematic structure of the optical module of the presentembodiment;

FIG. 4A shows a side view of a structure connecting a photoelectriccomponent and a high-speed signal input part;

FIG. 4B shows a perspective view of the structure shown in FIG. 4A;

FIG. 4C shows a front view of the photoelectric component seen from arelay board;

FIG. 4D shows a side view of the photoelectric component;

FIG. 4E shows an enlarged view of the relay board;

FIG. 5A shows a perspective view of the high-speed signal input part;

FIG. 5B shows a front view of the photoelectric component seen from therelay board;

FIG. 5C shows a side view of the photoelectric component;

FIG. 5D shows a view of the photoelectric component connected to a relayboard by an adhesive;

FIG. 6A shows a side view of an electrically conductive cap;

FIG. 6B shows a side view of another electrically conductive capprovided with a wave absorber;

FIG. 7A shows a side view of a high-speed signal circuit part 22;

FIG. 7B shows a bottom view of the high-speed signal circuit part;

FIG. 8A shows a structure fixing a low-speed signal processing part tothe high-speed signal processing part before the low-speed signalprocessing part is fixed;

FIG. 8B shows the structure shown in FIG. 8A after the low-speed signalprocessing part is fixed;

FIG. 9A shows a perspective view of a high-speed signal output part seenfrom an upper side;

FIG. 9B shows a perspective view of the high-speed signal output partseen from a lower side;

FIG. 9C shows a sectional side view of the high-speed signal outputpart;

FIG. 10A shows a perspective view of a surface-mount coaxial socket;

FIG. 10B shows a structure connecting the high-speed signal output partto a main board using the surface-mount coaxial socket before thehigh-speed signal output part is connected;

FIG. 11C shows the structure shown in FIG. 10B after the high-speedsignal output part is connected;

FIG. 11A shows a side view of a high-frequency coaxial socket;

FIG. 11B shows a structure connecting the high-speed signal output partand the main board by using the high-frequency coaxial socket;

FIG. 12 shows a second embodiment of a surface-mount coaxial socket; and

FIG. 13 shows a flow chart of an example of a process for producing theoptical module.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a side view of an embodiment of an optical module 1according to the present invention. As shown in FIG. 2, an opticalmodule 1 generally consists of a high-speed signal processing part 10which processes high-speed signals and a low-speed signal processingpart 11 which processes low-speed signals. The low-speed signalprocessing part 11 is disposed below the high-speed processing part 10,and mechanically and electrically connected thereto via connectingterminals 19 provided on the high-speed processing part 10. Since thehigh-speed signal processing part 10 and the low-speed signal processingpart 11 constitute a three-dimensional structure overlapping each otherin a vertical direction, an area occupied by the optical module 1 can bereduced.

The high-speed signal processing part 10 includes a high-speed signalinput part 21 for inputting photoelectrically converted high-speedsignals to a ceramic package, a high-speed signal circuit part 22contained in the ceramic package for processing the high-speed signalsinputted from the high-speed signal inputting part 21, and a high-speedsignal output part 23 for outputting the signals processed by thehigh-speed signal circuit part 22.

A photoelectric component 12, which is connected to the high-speedsignal input part 21 via a relay board 14, photoelectrically convertsoptical signals supplied from an optical fiber 13 and supplies theconverted signals to the high-speed signal input part 21. A cap 15,which is made of electrically conductive plastic or rubber, is mountedto cover an opening part of the high-speed signal input part 21 so thatthe inside of the high-speed signal input part 21 is electricallyshielded.

The high-speed signals inputted to the high-speed signal input part 21are supplied to the high-speed signal circuit part 22. The high-speedsignal circuit part 22 has a recess 18 provided on a center partthereof. A sealed space which is electrically shielded is formed bycovering the recess 18 with a lid 17 and providing a seal 16. The recess18 inside the sealed space contains a circuit which consists of SAWfilters, ICs, condensers and resistors for processing the high-speedsignals.

Relatively low-speed signals which need not be processed inside thesealed space are supplied to the low-speed signal processing part 11 viathe connecting terminal 19. The low-speed signal processing part 11includes, for example, a power supply control circuit, a stabilizationcontrol circuit and a phase fine-adjustment circuit. The low-speedsignal processing part 11 is implemented on a low-cost general-purposeprinted-circuit board in a double-sided or single-sided manner. Theconnecting terminal 19 has a flange 9. A position of the flange 9 isadjusted so that the low-speed signal processing part 11 is not tooclose to a bottom face of the high-speed signal processing part 10.Thus, it is possible to prevent the components implemented on the uppersurface of the low-speed signal processing part from being in contactwith the high-speed signal processing part 10.

The low-speed signal processing part 11 supplies processed signals tothe high-speed signal circuit part 22 via the connecting terminal 19.Thereafter, the high-speed signal circuit part 22 supplies processedsignals to the high-speed signal output part 23.

The high-speed signal output part 23 has a connecting terminal 20 forsupplying the signals outputted by the high-speed signal circuit part 22to a main board 8. Each of the high-speed signal output part 23 and thehigh-speed signal circuit part 22 comprises a multilayered board. Thehigh-speed signal output part 23 is connected to the high-speed signalcircuit part 22 so that the layered direction of the former isperpendicular to that of the latter. Thus, signals from the high-speedsignal circuit part 22 always flow along the layers of the multilayeredboards to the main board 8. In other words, a pseudo-planer electricalconnection can be achieved between the high-speed signal circuit part 22and the main board 8.

According to the above-mentioned structure, since the high-speed signalprocessing part 10 and the low-speed signal processing part 11 areseparately constructed, the volume of the sealed space can be decreased.Additionally, the low-speed signal processing part 11 can be implementedon an inexpensive printed-circuit board so that the cost of the opticalmodule 1 can be reduced

FIG. 3 shows a schematic structure of the optical module 1 of thepresent embodiment. As shown in FIG. 3, the optical module 1 consists ofthe high-speed signal processing part 10, the low-speed signalprocessing part 11 and the photoelectric component 12. As mentionedabove, since the high-speed signal processing part 10 and the low-speedsignal processing part 11 are separately constructed so that they areoverlapped with each other in a vertical direction, the size of theoptical module 1 is reduced by half as compared to a conventionaloptical module.

For example, a conventional optical module, which is shown by a chainline in FIG. 3, has a size of approximately 40 mm in length, 40 mm inwidth and 8.5 mm in height. On the other hand, the optical module 1 ofthe present invention has a size of 40 mm in length, 20 mm in width and8.5 mm in height. Thus, an area required to mount the optical module 1on the main board 8 can be halved as compared to the conventionaloptical module.

Now, further detailed descriptions will be given of each part of theoptical module 1 in accordance with a flow of a signal in the opticalmodule 1.

<High-speed Signal Input Part>

FIG. 4A shows a side view of a structure connecting the photoelectriccomponent 12 and the high-speed signal input part 21, FIG. 4B shows aperspective view of the structure shown in FIG. 4A, FIG. 4C shows afront view of the photoelectric component 12 seen from the relay board14, FIG. 4D shows a side view of the photoelectric component 12, andFIG. 4E shows an enlarged view of the relay board 14.

In the structure shown in FIGS.4A to 4E, the photoelectric component 12has five straight leads 24 including one lead for a signal line, threeleads for power supply lines and one lead for a ground line. Generally,the leads 24 of the photoelectric component 12 are not arranged in thesame plane. The relay board 14 has a function of connecting the straightleads 24 to a planar board of the high-speed signal input part 21without bending the straight leads 24.

FIG. 4E shows through holes 25 to 33 provided on the relay board 14. Thelead 24 for a signal line is positioned at a position corresponding tothe through hole 25, the leads 24 for power supply lines are positionedat positions corresponding to the through holes 26, 28, 29 and the lead24 for a ground line is positioned at a position corresponding to thethrough hole 27, for example.

The lead 24 for a signal line passes through the through hole 25 and isdirectly connected to a corresponding signal terminal of the high-speedsignal input part 21. The three leads 24 for power supply lines areconnected to the through holes 26, 28, 29, respectively. The throughholes 26, 28, 29 are connected to the through holes 31, 32, 33,respectively, via patterns provided on the relay board 14. The throughholes 31, 32, 33 are connected to corresponding signal terminals of thehigh-speed signal input part 21 via leads. The lead 24 for a ground lineis connected to the through hole 27. The through hole 27 is connected tothe through hole 30 via a pattern provided on the relay board 14. Thethrough hole 30 is connected to a corresponding signal terminal of thehigh-speed signal input part 21 via a lead.

According to the above-mentioned structure, the straight leads 24 of thephotoelectric component 12 can be connected to the signal terminalsprovided on a planar board of the high-speed signal input part 21 byproviding the relay board 14. Additionally, since the lead for a signalline is directly connected to the corresponding signal terminal of thehigh-speed signal input part 21, a transmission loss of the weakhigh-speed signals can be reduced.

FIG. 5A to 5C show an example of a structure fixing the photoelectriccomponent 12. FIG. 5A shows a perspective view of the high-speed signalinput part 21, FIG. 5B shows a front view of the photoelectric component12 seen from the relay board 14, and FIG. 5C shows a side view of thephotoelectric component 12.

As shown in FIGS. 5B and 5C, the photoelectric component 12 has a flange36 for mechanically fixing the photoelectric component 12 to thehigh-speed signal input part 21 by screws. The flange 36 has notchesprovided on both sides thereof. Through these notches, screws arethreaded into threaded holes 35 provided on a U-shaped block 37 of thehigh-speed signal input part 21 so that the photoelectric component 12is fixed to the high-speed signal input part 21.

A state in which the photoelectric component 12 is fixed to thehigh-speed signal input part 21 is shown in the above-mentioned FIGS. 4Aand 4B. In this state, the flange 36 may be bent since the flange has athin shape. As shown in FIG. 5C, the relay board 14 is disposed apartfrom the flange 36. According to this structure, the relay board 14 isnot affected by the bending of the flange 36 or stresses generated bythe screws. The same effect can be also obtained by providing softinsulating adhesive (for example, silicone adhesive or epoxy adhesivehaving low elasticity) between the relay board 14 and the photoelectriccomponent 12.

This use of the soft insulating adhesive between the relay board 14 anthe photoelectric component 12 is illustrated in FIG. 5D

FIG. 6A shows aside view of the electrically conductive cap 15 whichcloses an opening part of the high-speed signal input part 21, and FIG.6B shows a similar side view showing a wave absorber 43 provided on alower face of the electrically conductive cap 15.

As shown in FIGS. 6A and 6B, the high-speed signal input part 21 has anopening part 40 for soldering the lead 24 for a signal line of thephotoelectric component 12 or the leads from the relay board 14 to thecorresponding signal terminals when the photoelectric component 12 isfixed. According to the structures shown in FIG. 6A, an electric shieldcan be achieved by closing the opening part 40 with the electricallyconductive cap 15. Additionally, according to the structure shown inFIG. 6B, the performance of the electric shield can be further improvedby providing the wave absorber 43 on a lower side of the electricallyconductive cap 15.

The electrically conductive cap 15 has a projecting part which can befitted into the opening part 40. An outwardly projecting claw 41 isprovided on the tip of the projecting part. On the other hand, thehigh-speed signal input part 21 has a recess 42 provided on the sidewall of the opening at a position corresponding to the claw 41. Theelectrically conductive cap 15 is fixed to close the opening by engagingthe claw 41 with the recess 42. According to this structure, theelectrically conductive cap 15 can be removed after having been fixed,and thus the photoelectric component 12 can be easily replaced.

<High-speed Signal Circuit Part>

FIG. 7A shows a side view of the high-speed signal circuit part 22, andFIG. 7B shows a bottom view of the high-speed signal circuit part 22. Asshown in FIG. 7A, the high-speed signal circuit part 22 has the recess18 on a center part thereof. The recess 18 is covered with the lid 17and the seal 16 is provided to form a sealed space which is electricallyshielded. A circuit which consists of components such as SAW filters,ICs, condensers and resistors is provided on the bottom face of therecess 18 inside the sealed space. This circuit processes high-speedsignals supplied from the high-speed signal input part 21.

Additionally, the high-speed signal circuit part 22 has a circuitadjustment part which consists of pattern parts 45, 46 and patternconnecting lines 47 provided outside the sealed space (for example, on abottom face of the high-speed signal circuit 22) for adjusting the ICsprovided in the sealed space. Operations of the ICs inside the sealedspace can be adjusted by connecting or disconnecting the pattern part 45and the pattern part 46 by the pattern connecting lines 47.

<Low-speed Signal Circuit Part>

FIGS. 8A and 8B show a structure fixing the low-speed signal processingpart 11 to the high-speed signal processing part 10. FIG. 8A shows thestructure before the low-speed signal processing part 11 is fixed, andFIG. 8B shows the structure after the low-speed signal processing part11 is fixed.

As shown in FIGS. 8A and 8B, the connecting terminal 19 provided on thebottom face of the high-speed signal processing part 10 has a thick part19 a near the tip thereof. The maximum outside diameter O of the thickpart 19 a satisfies the following equation (1).

O=O _(typ) ±A  (1)

Additionally, the inside diameter of a through hole 48 provided in thelow-speed signal processing part 11 in which the connecting terminal 19is inserted satisfies the following equation (2).

H=H _(typ) ±B  (2)

The connecting terminal 19 and the through hole 48 are constructed sothat the following equation (3) is satisfied.

O _(typ) =H _(typ) +A+B  (3)

In this case, the tolerances A and B are very small values, and thus theoutside diameter of the thick part 19 a is slightly larger than theinside diameter of the through hole 48. When the connecting terminal 19is inserted in the through hole 48, the thick part 19 is resilientlydeformed so that it can pass through the through hole 49.

According to the above-mentioned structure of the connecting terminal 19and the through hole 48, if solder connecting the connecting terminal 19to the through hole 48 is melted when the optical module 1 is mounted onthe main board 8, the low-speed signal processing part 11 can beprevented from falling down by the thick part 19 a of the connectingterminal 19 engaging with the circumferential part of the through hole48.

<High-speed Signal Output Part>

FIG. 9A shows a perspective view of the high-speed signal output part 23seen from an upper side, FIG. 9B shows a perspective view of thehigh-speed signal output part 23 seen from a lower side, and FIG. 9Cshows a sectional side view of the high-speed signal output part 23.

As mentioned above, each of the high-speed signal output part 23 and thehigh-speed signal circuit part 22 comprises a multi-layered ceramicboard, and the layered direction of the multilayered boards areperpendicular to each other.

As shown in FIG. 9A, the high-speed signal output part 23 is providedwith signal bumps 50 for transmitting high-speed signals. Additionally,a plurality of ground bumps 51 are provided around each of the signalbumps 50. The high-speed signal output part 23 is electrically connectedto the high-speed signal circuit part 22 via the bumps 50 and 51.

The signal bumps 50 and the ground bumps 51 are connected to signalpatterns 54 and ground patterns 55, respectively. The patterns 54, 55extend along the layers of the multilayered board. The signal patterns54 are connected to the main board 8 via a connecting terminal 52 fortransmitting high-speed signals, and the ground patterns 55 areconnected to connecting terminals 53 for grounding provided around eachof the connecting terminals 52. The high-speed signal output part 23 hasa height h corresponding to a distance between the high-speed signalcircuit part 22 and the main board 8.

According to the above-mentioned structure, since the high-speed signalcircuit part 22 is electrically connected to the main board 8 in apseudo-planar manner, that is, the signals from the high-speed signalcircuit part 22 always flow along the layers of the circuit boards tothe main board 8, an impedance matching can be easily achieved.Additionally, since the high-speed signal output part 23 connects thehigh-speed signal circuit part 22 to the main board 8 in a coaxialmanner with the ground pattern 55 being disposed on both sides of thesignal pattern 54 transmitting high-speed signals, transmission loss canbe reduced.

FIG. 10A shows a perspective view of a surface-mount coaxial socket 60,FIG. 10B shows a structure connecting the high-speed signal output part23 to the main board 8 using the surface-mount coaxial socket 60 beforethe high-speed signal output part 23 is connected, and FIG. 10C showsthe structure shown in FIG. 10B after the high-speed signal output part23 is connected.

As shown in FIGS. 10A to 10C, the surface-mount coaxial socket 60comprises a through hole 61 and a ground part 62 provided around thethrough hole 61. The connecting terminal 20 is inserted into a throughhole 63 of the main board 8 through the through hole 61 of thesurface-mount coaxial socket 60. On the other hand, the ground part 62of the surface-mount coaxial socket 60 is connected to a ground part 64of the main board 8. According to this structure, since the ground part62 is positioned around the connecting terminal 20 for outputtinghigh-speed signals, an effect of a coaxial connection can be obtained.

FIG. 1A shows a side view of a high-frequency coaxial socket 66 whichcan be used instead of the surface-mount coaxial socket 60, and FIG. 11Bshows a structure connecting the high-speed signal output part 23 to themain board 8 by using the high-frequency coaxial socket 66.

As shown in FIGS. 11A and 11B, the high-frequency coaxial socket 66comprises a receiving opening 67, a ground part 68 provided around thereceiving opening 67, an electrode 69 provided at the bottom of thereceiving opening 67, and a bump 71 for connecting the ground part 68 toa ground part 70 provided on the high-speed signal output part 23. Thereceiving opening 67 receives a connecting terminal 65 of the high-speedsignal output part 23 and resiliently fixes a thick part 65 a at the tipof the connecting terminal 65.

The electrode 69 of the high-frequency coaxial socket 66 is insertedinto a through hole 73 and connected thereto by soldering, so that theconnecting terminal 65 is electrically connected to the main board 8.Additionally, the ground part 68 of the high-frequency coaxial socket 66is connected to a ground part 74 provided on the main board 8. Accordingto the above-mentioned structure, since the ground part 68 is positionedaround the connecting terminal 65 for outputting high-speed signals, aneffect of a coaxial connection can be obtained.

FIG. 12 shows a second embodiment of a surface-mount coaxial socket. InFIG. 12, those parts which are the same as the parts shown in FIGS. 10Ato 10C are given the same reference numerals, and descriptions thereofwill be omitted.

As shown in FIG. 12, a surface-mount coaxial socket 75 is constructed sothat the tip of a connecting terminal 76 for outputting high-speedsignals inserted into the through hole 61 is positioned on the sameplane as the bottom surface of the coaxial socket 75. A land 77 isprovided on the main board 8 at a position corresponding to the tip ofthe connecting terminal 76 and the connecting terminal 76 is connectedto the land 77. According to the above-mentioned structure, since theground part 62 is positioned around the connecting terminal 76 foroutputting high-speed signals, an effect of a coaxial connection can beobtained. Additionally, the coaxial socket 75 can constitute a perfectsurface mount structure in which the socket 75 is connected to the mainboard 8 only on the surface of the main board 8.

Now, a description will be given of a process for producing the opticalmodule 1. FIG. 13 shows a flow chart of an example of a process forproducing the optical module 1. As shown in FIG. 13, the processcomprises a process for producing the low-speed signal processing part11 (S10 and S12), a process for producing the high-speed signalprocessing part 10 (S20 and S22), and a process for assembling theoptical module 1 (S30 to S34).

In step S10, components constituting the low-speed signal processingpart 11 are mounted on an inexpensive printed-circuit board. In thisstep S10, double-sided surface mount is used to mount the components onthe printed-circuit board so that a cost for mounting the components canbe reduced. Additionally, since the components are mounted before theprinted-circuit board is cut off, a production time can be shortened andthe cost can be further reduced. In step S12 subsequent to step S10, theprinted-circuit board is cut into boards, each of which constitutes thelow-speed signal processing part 11.

In step S20, components constituting the high-speed signal processingpart 10 are mounted in a ceramic package. Then, in step S22, the ceramicpackage is sealed.

In step S30 subsequent to steps S12 and S22, the low-speed signalprocessing part 11 produced in steps S10, S12 and the high-speed signalprocessing part 10 produced in steps S20, S22 are connected via theconnecting terminal 19 provided on the high-speed signal processing part10.

In step S32 subsequent to step S30, the photoelectric component 12 ismounted to the high-speed signal processing part 10 and the electricallyconductive cap 15 is mounted to cover the opening part 40 where thephotoelectric component 12 is connected so that an electric shield canbe achieved. In step S34, the optical module 1 produced by the processin steps S10 to S32 is mounted on the main board 8.

Since the optical module 1 produced by the above-mentioned processconsists of the high-speed signal processing part 10 and the low-speedsignal processing part 11 which are separately produced, the plasticpackage of the high-speed signal processing part 10 which requires asealing can be miniaturized. Additionally, since an inexpensiveprinted-circuit board is used to constitute the low-speed signalprocessing part 11, double-sided surface mount can be used. Thus,according to the optical module 1 of the present embodiment, it ispossible to achieve miniaturization and cost reduction of the opticalmodule 1.

The present invention is not limited to these embodiments, butvariations and modifications may be made without departing from thescope of the present invention.

The present application is based on Japanese priority application No.10-298867 filed on Oct. 20, 1998, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part on a printed circuit board different from the high-speed signal processing part, with the low-speed processing part processing a low-speed signal and supplying a processed low-speed signal to the high-speed signal processing part, wherein said high-speed signal processing Part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part, with the optical module further comprising: a relay board for converting an arrangement of leads of said photoelectric component into an arrangement of input terminals of said high-speed signal input part.
 2. The optical module as claimed in claim 1, wherein said relay board is disposed apart from said photoelectric component.
 3. The optical module as claimed in claim 2, wherein insulating soft adhesive is provided between said relay board and said photoelectric component.
 4. The optical module as claimed in claim 2, wherein a lead of said photoelectric component for outputting a signal is positioned on a plane which includes the input terminals of said high-speed signal input part and directly connected to said input terminals without being connected to said relay board.
 5. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part on a printed circuit board different from the high-speed signal processing part, with the low-speed processing part processing a low-speed signal and supplying a processed low-speed signal to the high-speed signal processing part, wherein said high-speed signal processing part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part, wherein said high-speed signal input part comprises: an opening part in which input terminals are exposed; and an electrically conductive cap which closes said opening part.
 6. The optical module as claimed in claim 5, wherein a wave absorber is provided on a bottom side of said cap.
 7. The optical module as claimed in claim 5, wherein said cap is provided with an outwardly projecting claw and said high-speed signal input part is provided with a recess which can be engaged with said claw.
 8. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part on a printed circuit board different from the high-speed signal processing part, with the low-speed processing part processing a low-speed signal and supplying a processed low-speed signal to the high-speed signal processing part, wherein said high-speed signal processing part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part wherein said high-speed signal circuit part is mounted in a recess provided on a package, which recess is sealed by a cap to electrically shield said high-speed signal circuit part.
 9. The optical module as claimed in claim 8, wherein a circuit adjustment part for adjusting an integrated circuit in said high-speed signal circuit part is provided outside the part sealed by said cap.
 10. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part which processes a low-speed signal, wherein said high-speed signal processing part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part, wherein said high-speed signal circuit part is mounted in a recess provided on a package, which recess is sealed by a cap to electrically shield said high-speed signal circuit part, and wherein a connecting terminal of said high-speed signal processing part for connecting to said low-speed signal processing part has a thick part whose maximum outside diameter O is O_(typ)±A, and the low-speed signal processing part is provided with a through hole in which said connecting terminal is inserted which through hole has an inside diameter H equal to H_(typ)±B, wherein a relationship O_(typ)=H_(typ)+A+B is satisfied.
 11. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part on a printed circuit board different from the high-speed signal processing part, with the low-speed processing part processing a low-speed signal and supplying a processed low-speed signal to the high-speed signal processing part, wherein said high-speed signal processing part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part wherein each of said high-speed signal output part and high-speed signal circuit part comprises a multilayered board, said multilayered board of the high-speed signal output part having a length corresponding to a distance between said high-speed signal circuit part and a main board and being connected to said multilayered board of said high-speed signal circuit part so that the layered directions of said multilayered boards are perpendicular to each other.
 12. The optical module as claimed in claim 11, wherein said multilayered board of said high-speed signal output part is provided with a signal pattern for transmitting signals and a plurality of ground patterns provided on both sides of said signal pattern.
 13. The optical module as claimed in claim 12, wherein said high-speed signal output part comprises: a bump for electrically connecting said high-speed signal output part to said high-speed signal circuit part; and a connecting terminal for connecting said high-speed signal output part to said main board.
 14. The optical module as claimed in claim 13, wherein said bump consists of a signal bump for transmitting signals and a plurality of ground bumps provided around said signal bump.
 15. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part which processes a low-speed signal, wherein said high-speed signal processing part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part, and wherein said high-speed signal output part has a high-frequency coaxial socket which connects said high-speed signal output part to a main board.
 16. The optical module as claimed in claim 15, wherein said high-speed signal output part is provided with a connecting terminal having a thick part for outputting signals, wherein said high-frequency coaxial socket comprises: a receiving opening which receives and resiliently fixes said thick part; a bump which is resiliently engaged with a ground part provided around said connecting terminal of said high-speed signal output part; a signal electrode provided at the bottom of said receiving opening; and a ground electrode provided around said signal electrode, said signal electrode and said ground electrode being connected to said main board.
 17. An optical module comprising: a photoelectric component; a high-speed signal processing part which processes a high-speed signal photoelectrically converted by said photoelectric component; and a low-speed signal processing part which processes a low-speed signal, wherein said high-speed signal processing part and said low-speed signal processing part are overlapped with each other in a vertical direction and electrically connected to each other, wherein said high-speed signal processing part comprises: a high-speed signal input part for inputting said high-speed signal; a high-speed signal circuit part for processing said high-speed signal inputted to said high-speed signal input part; and a high-speed signal output part for outputting the signal processed by said high-speed signal circuit part, and wherein said high-speed signal output part has a surface-mount coaxial socket which comprises: a through hole which connects a connecting terminal provided on said high-speed signal output part to a main board; and a ground part provided around said through hole and connected to a ground part of said main board.
 18. The optical module as claimed in claim 17, wherein a tip part of said connecting is positioned on the same plane as a bottom surface of said surface-mount coaxial socket and connected to a corresponding land provided on said main board. 